link fix_REL-3.1.1.2/fix to avoid super long downloading time (#197)

CRTMv3 code changed the behavior on how to find the local coefficient
fix files. It requires an existing `fix/` under the bundle directory.

Otherwise it will automatically start a downloading process to fetch a
tarball file from
`https://bin.ssec.wisc.edu/pub/s4/CRTM//fix_REL-3.1.1.2.tgz` and
unzip/untar it.

This downloading process is very slow. I tried it on Hera and Jet
recently and the download speed is about 400kb~800kb/s while the file
size is 7.3G. Anyone wants to experience this pain can try as follows,
:)
```
wget https://bin.ssec.wisc.edu/pub/s4/CRTM//fix_REL-3.1.1.2.tgz
tar xvf fix_REL-3.1.1.2.tgz
```

This PR creates that simple link (pointing to staged data under the
`RDAS_DATA` directory) and eliminate that pain.

It does not affect any current RDASApp functionalities, but supports a
smooth build process when one want to replace `sorc/crtm` with CRTMv3 in
his/her own offline play.

Co-authored-by: Samuel Degelia <[email protected]>

.gitignore

@@ -154,6 +154,7 @@ install*/
 !/bundle/ioda-data
 !/bundle/fv3-jedi-data
 !/bundle/mpas-jedi-data
+!/bundle/fix
 
 # 
 expr

bundle/fix

@@ -0,0 +1 @@
+../fix/crtm/fix_REL-3.1.1.2/fix